Interchangeable orifice plate wellhead system

ABSTRACT

An interchangeable orifice wellhead system is disclosed which comprises a flow control valve comprised of a male union, a female union, a valve cap, and an orifice plate. The orifice plate can include a display tab, which visually communicates to the technician the size of orifice plate aperture. Orifice plates having different size apertures can be interchanged within the same flow control valve. In some embodiments, the male union of the flow control valve can be machined or interchanged with another male union to be used with different size orifice plates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/014,938, which was filed on Jun. 20, 2014, andentitled “Orifice Plate Wellheads.” The disclosure of the foregoingapplication is hereby incorporated by reference in its entirety.

BACKGROUND

The present technology relates to orifice plate wellhead systems and, inparticular, orifice plate wellhead systems configured to easilydetermine and/or adjust the flow rate of fluid.

Most landfill gas is produced by biodegradation, which occurs whenorganic waste is broken down by bacteria naturally present in the wasteand in the soil used to cover the landfill. Landfill gas is mostly madeof methane, carbon dioxide, and trace amount of a wide variety ofvolatile organic compounds.

Landfill gases can contribute to ozone formation, atmosphericphotochemical reaction, and other types of air pollution. Landfill gasescan also create dangerous conditions. For example, if methane is presentin the air at higher concentrations, it can be explosive. Landfill gasesmay also contribute to water pollution if it migrates and comes incontact with groundwater. Therefore, it is desirable to collect landfillgas to prevent these dangers. Collected landfill gases can be used as asource of power generation, or be incinerated before being released intothe atmosphere.

Active landfill gas well extraction systems are used to collect landfillgases. Such systems are commonly made of an array of pipes and valves influid communication with a vacuum source. Active landfill gas wellextraction systems also include wellhead assemblies, which are used tomonitor and control the amount of gas passing through the pipes. Awellhead assembly can include flow rate measurement sensors and a flowrate control feature, which are used to determine and control the gasextraction rate.

One of the important considerations in using a gas well extractionsystem is to precisely control the gas flow rate. Under-extraction ratesmean the extraction rate is not high enough to prevent gas from reachingthe surface or prevent subsurface migration. This may result in airpollution or a fire hazard. Over-extraction rates mean the extractionrate is high enough to draw large amounts of air into the waste column.This may kill many of the microorganisms, resulting in reduced methanerecovery. Thus, the gas flow rate needs to be carefully monitored andcontrolled within a narrow operating range to prevent over- orunder-extraction of landfill gas.

SUMMARY

The systems, methods and devices described herein have innovativeaspects, no single one of which is indispensable or solely responsiblefor their desirable attributes. Without limiting the scope of theclaims, some of the advantageous features will now be summarized.

One aspect of the present invention is the realization that existing gasvalves do not provide the capability for a technician to accuratelydetermine and finely tune the flow rate of gas through the wellheadsystems in the field. Thus, there exists a need for a wellhead systemwhich allows for accurate determination and tuning of gas flow rate inthe field. Described herein are various implementations of orificeplates that may be used for course adjustment of flow rates of awellhead's gas flow rate, or even fine adjustment of flow rates in someembodiments. In some embodiments, another flow rate mechanism, such asthe needle valve described in U.S. Pat. No. 8,678,348, titled “GAS FLOWCONTROL VALVE,” issued Mar. 25, 2014, may be used in conjunction withthe flow rate control mechanisms discussed herein. The above-notedpatent is hereby incorporated by reference in its entirety and for allpurposes.

In one embodiment, a flow control valve comprises a male unioncomprising a male threaded portion and a central aperture configured toallow gas flow within the central aperture, a valve cap membercomprising a female threaded portion configured to receive andthreadedly engage with the male threaded portion of the male union, andan orifice plate configured for positioning between the male union andthe valve cap member, such that the orifice plate is securedly engagedbetween the male union and the valve cap member when threadedly engaged,the orifice plate including a substantially circular plate having anorifice in a central portion of the substantially circular plate, theorifice plate further including a tab portion extending substantiallyorthogonal to a plane of the substantially circular plate, the tabportion including a visual indication of a size of the orifice in thecentral portion of the substantially circular plate. In one embodiment,the male threaded portion includes a size indication slot extendingacross all of threads of the male threaded portion along less thantwenty percent of an outer circumference of the male union, the sizeindication slot sized to allow at least a portion of the tab portion ofthe orifice plate to be enclosed between threads of the female threadedportion and the size indication slot of the male threaded portion.

The flow control valve may comprise a female union comprising a centralaperture configured to allow gas flow within the central aperture. Theorifice plate may be securedly engaged between the male union and thefemale union. The flow control valve may further comprise a sealingmeans for sealing a space between the male union and the valve capmember. The flow control valve may further comprise a sealing means forsealing a space between the male union and the female union. The sealingmeans may be an o-ring. The sealing means may further comprise the valvecap member. The flow control valve may comprise a top surface having arecessed ledge configured to receive the orifice plate therein. Therecessed ledge may further comprise an o-ring groove, the o-ring groovebeing shaped and sized to fit an o-ring. The orifice plates may havedifferent size orifices that can be interchanged within said recessedledge. The tab portion of the orifice plate may have widths of betweenabout 0.3 and 1.5 inches. The orifice plate may have an orifice diameterof between about 0.3 and 3.0 inches.

In one embodiment, a retrofit kit for a flow control valve in a wellheadsystem comprises a plurality of interchangeable orifice plates eachincluding a substantially circular plate having an orifice in a centralportion of the substantially circular plate and a tab portion extendingsubstantially orthogonal to a plane of the substantially circular plate,the tab portion including a visual indication of a size of the orificein the central portion of the circular plate. In one embodiment, atleast two of the interchangeable orifice plates have orifices ofdifferent sizes. In one embodiment, the retrofit kit further includes amale union comprising a male threaded portion, a top planar surface, anda central aperture configured to allow gas flow within the centralaperture, the top planar surface of the mail union including a recessedledge shaped and sized to allow the interchangeable orifice plates to beremovably mounted to the orifice plate recess, the male union furthercomprising a size indication slot extending across all threads of themale threaded portion along less than twenty percent of an outercircumference of the male union, the size indication slot sizedconfigured to allow at least a portion of the tab portion of the orificeplate to be enclosed between threads of the female threaded portion andthe size indication slot of the male threaded portion, wherein the maleunion is configured to replace a widely used male union of existinglandfill flow control valves.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects, as well as other features, aspects, andadvantages of the present technology will now be described in connectionwith various embodiments, with reference to the accompanying drawings.The illustrated embodiments, however, are merely examples and are notintended to be limiting. Like reference numbers and designations in thevarious drawings indicate like elements.

FIG. 1 is an isometric drawing of an exemplary wellhead system.

FIG. 2 is an isometric drawing of a wellhead system including a flowcontrol valve with an orifice plate having a display tab.

FIG. 3 illustrates an exploded view of the flow control valve shown inFIG. 2.

FIG. 4 illustrates a perspective view of one embodiment of a male union.

FIG. 5 illustrates a cross-section view of one embodiment of a maleunion.

FIGS. 6A to 6D illustrate example orifice plates having variousapertures.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the present disclosure. Theillustrative embodiments described in the detailed description,drawings, and claims are not meant to be limiting. Other embodiments maybe utilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented here. It will be readilyunderstood that the aspects of the present disclosure, as generallydescribed herein, illustrated in the figures, can be arranged,substituted, combined, and designed in a wide variety of differentconfigurations, all of which are explicitly contemplated and form partof this disclosure. For example, a system or device may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, such a system or device may be implemented or sucha method may be practiced using other structure, functionality, orstructure and functionality in addition to or other than one or more ofthe aspects set forth herein. Alterations in further modifications ofthe inventive features illustrated herein, and additional applicationsof the principles of the inventions as illustrated herein, which wouldoccur to one skilled in the relevant art in possession of thisdisclosure, are to be considered within the scope of the invention.

Descriptions of the necessary parts or elements may be omitted forclarity, and like reference numerals refer to like elements throughout.In the drawings, the size and thickness of layers and regions may beexaggerated for clarity and convenience.

Embodiments described herein generally relate to systems, devices, andmethods related to orifice plate wellhead systems. More specifically,some embodiments relate to orifice wellhead systems configured to easilydetermine and/or adjust the flow rate of fluid, such as gas. When usedherein, flow rate is used in reference to the volumetric flow ratepassing through the flow control valve.

FIG. 1 is an isometric view of one embodiment of an orifice wellheadsystem 100. As noted above, an operating goal of landfills is to removegas at the approximate rate of its generation. Therefore, in someembodiments, the orifice wellhead system 100 can comprise a flow controlvalve 120 as illustrated in FIG. 1. The orifice wellhead system 100 caninclude an upper pipe 140, a lower pipe 160, and the flow control valve120. In some embodiments, gas may be extracted from the landfill andflow through the lower pipe 160 past the flow control valve 120 to reachthe upper pipe 140. Often, the flow control valve 120 can allow atechnician to adjust the rate of gas flowing through the valve and thusthe rate of gas extraction. The flow control valve 120 is configured toaccurately set the flow rate of gas flowing through the flow controlvalve 120, especially when the desired rate of extraction and, thus thedesired flow rate through the flow control valve 120 is low and/or whena precise flow rate and/or a small adjustment to the current flow rateof the wellhead are necessary.

FIG. 2 is an isometric drawing of a wellhead including a flow controlvalve 220 that includes an orifice plate with a display tab 250. Theterm “valve,” as well as other terms used herein, should be construed toinclude the provided definitions, the ordinary and customary meaning ofthe terms, and/or any other implied meaning for the respective terms.The valve 220, for example, may also be referred to as a housing fororifice plates or an orifice plate retaining assembly. Accordingly, useof “valve” herein is simply for ease of description and does not limitthe scope of the term to external uses/definitions of the term.

In some embodiments, the flow control valve 220 includes a display tab250 (that is part of an interchangeable orifice plate, as describedfurther below) that visually communicates to the technician a setting ofthe flow control valve 220, such as a diameter of an aperture in theparticular orifice plate currently included in the flow control valve220. In the example of FIG. 2, for example, an aperture size of “1.0” isindicated on the display tab 250, which in this example indicates thatan orifice within the flow control valve 220 has a diameter of 1 inches.In other embodiments, the orifice size indicator may be in a differentformat, such as a letter, color, symbol, etc. representing a size oforifice. By using a display tab 250 a technician is able to moreaccurately determine a current flow rate and determine when and whichadjustment are to be made. As necessary, the technician may adjust gasflow through the wellhead by adjusting the orifice plate included withinthe flow control valve 220 to achieve a new, desired flow setting (whichwill then be displayed external to the flow control valve 220 on adisplay tab 250 of a replacement orifice plate).

FIG. 3 illustrates an exploded view of the flow control valve shown 220in FIG. 2, and FIG. 4 illustrates a perspective view of one embodimentof the male union 230 (of FIGS. 2-3) that includes a size indicationslot 320 (e.g., that is machined into an existing male union and/or isincluded in an originally molded male union) that is sized to containthe display tab 250 of an orifice plate 210. In the example of FIG. 3,the flow control valve 120 includes a tabbed orifice plate 210, ano-ring 270, a male union 230, a female union 240, and a valve cap member260. As shown in FIG. 3, each of the parts comprising the flow controlvalve 220 can be joined together axially.

FIGS. 6A to 6D illustrate additional tabbed orifice plates 210A, 210B,210C, and 210D having various aperture sizes. In this example, thetabbed orifice plates 510 are washer-shaped plates having an outerdiameter 510 and an orifice (also referred to herein as an “aperture”)520. As shown, each of the tabbed orifice plates 210 includes a displaytab 250 (250A, 250B, 250C, and 250D, respectively). The display tab 250can be a flat rectangular plate extending substantially orthogonal froma planar surface of the orifice plate 210, on or near the outer diameter510 of the orifice plate 210. In some embodiments, the display tab 250can extend substantially orthogonal from a rectangular plate on theplanar surface 215 (FIG. 3) of the orifice plate 210, away from theouter diameter 510 of the orifice plate 210.

Returning to FIG. 3, the illustrated o-ring 270 is a ring-shaped bandmade of an elastomer. The female union 240 can be substantiallycylindrical in shape, having a central aperture. The male union 230 canbe substantially cylindrical in shape configured to couple with thefemale union 240 (e.g. by receiving the female union 240 within theperimeter wall 335 as described below with reference to FIG. 5). Themale union 230 can have central aperture. Central apertures of the maleand female unions 230, 240 are configured to allow gas flow within thecentral aperture.

The valve cap member 260 can be substantially cylindrical in shapehaving an internal cylindrical bore. The internal cylindrical bore ofthe valve cap member 260 can have a greater circumference than thecircumference of the male union 230 and the female union 240, whichallows the male union 230 and the female union 240 to slip-fit into theinternal bore of the valve cap member 260. The valve cap member 260 caninclude a top latching portion 262 and a valve cap threaded portion 265.The valve cap threaded portion 265 can be internal threads on the innercircumferential surface of the valve cap member 260 generally on thebottom half of the valve cap member 260. The orifice plate 210 can beaxially positioned between the male union 230 and the female union 240,with the display tab 250 extending towards the male union 230. Theo-ring 270 can be axially positioned between the male union 230 and theorifice plate 210.

Parts of the flow control valve 220 described above in reference to FIG.3 can be positioned differently along the axis. For example, in someembodiments, the male union 230 is axially positioned above the femaleunion 240. In some embodiments, the display tab 250 can extend towardsthe female union 240. In some embodiments, the valve cap member 260 canthreadingly mate with the female union 240. In some embodiments, thevalve cap member 260 and female union 240 may be combined into a singlecomponent. Other configurations with different combinations,separations, and/or positionings of parts are possible, and suchconfigurations are within the scope of this disclosure.

Referring to FIGS. 4 and 5 (FIG. 5 is a cross-section of the male union230 taken across section 5-5 indicated in FIG. 4), the male union 230can include a male union threaded portion 340, a top surface portion315, and a size indication slot 320. The threaded portion 340 can beexternal threads on the outer circumferential surface of the male union230. The threaded portion 340 can be generally on the top half of themale union, and comprises the outermost circumference of the male union.The top surface portion 315 can be a ring-shaped surface portionperpendicular to the axial direction of the male union, formed by aslight reduction of diameter on the top edge of the male union. The sizeindication slot 320 can be a rectangular cutout on the threaded portion340 extending across all of threads of the male threaded portion, shapedand sized to fit the display tab 250 of the orifice plate 210. The sizeindication slot 320 can extend along less than twenty percent of acircumference of the male union. In one embodiment, the size indicationslot 320 extends along a circumference of the male union a distance thatis substantially equivalent to a width of the display tab 250. Forexample, if the display tab 250 width is 0.53 in, the size indicationslot 320 may be slightly larger than 0.53 in (e.g., 0.54 in) such thatthe size indication slot 320 secures the display tab 250 within the sizeindication slot 320. In some embodiments, the size indication slot 320can cut into the male union threaded portion 340 with a depth that isdeeper than the thickness of the display tab 250. For example, the sizeindication slot 320 can have a depth of between about 0.06 in to about0.1 in.

The valve cap member 260 can be axially positioned above the femaleunion 240 and threadingly mate with the male union 230. For example, thevalve cap member 260 can mate with the male union 230 by screwing thevalve cap member 260 onto the male union 230, by threadingly mating thevalve cap threaded portion 265 with the male union threaded portion 340.In some embodiments, the height of the valve cap member in the axialdirection can be shorter than the height of the male union 230 and thefemale union 240. For example, as shown in FIG. 2, parts of the maleunion 230 and the female union 240 are exposed and not covered by thevalve cap member 260. The axial length of the display tab 250 can besimilar to the axial height of the male union 230, such that a portionof the display tab 250 is visible when the valve cap member 260 is matedto the male union 230. In some embodiments, as shown in FIGS. 1 and 2,the top latching portion 262 of the valve cap member 260 can latch ontoa portion of the female union member 240, while the valve cap member 260threading mates with the male union 230, thereby securing the femaleunion 240 with the male union 230. By securing the female union 240 andthe male union 230, the space between the male and female unions can betightened and sealed.

Visible Tab

In some embodiments, a display tab 250 may allow a technician to confirmthe aperture reading from the outside of the flow control valve 120during the operation of the orifice wellhead system 100. An unobstructedview of the tab can allow the technician to view the aperture readingwithout having to manually adjust any features, such as a valve sealingcap. Sometimes a technician may need to connect and operate a gas flowsensor to orifice wellhead systems in order to determine gas flow rateswithin a pipe. With a display tab 250 visible from the outside, thetechnician may read the aperture and connect the sensor to pressureports on the wellhead system and determine the gas flow rateimmediately, without having to unscrew, remove or adjust any obstructingfeatures.

In some embodiments, a valve cap member can be used on a flow controlvalve 220. The valve cap member 260 may cover only a portion of thedisplay tab 250, such that a portion of the display tab 250 showing theaperture 520 of the orifice plate 210 remains visible even after thevalve cap 260 is screwed in on the male union 230. A technician canconfirm the reading on the display tab 250, unscrew the valve cap member260, and replace the orifice plate 210 with another orifice plate havinga different aperture (such as the example orifice plates 210A-210Dillustrated in FIG. 6). The valve cap member 260 can serve both toconnect the male and female unions 230, 240, and to tighten and seal thespace between the male and female union with the orifice plate 210 inbetween. With the valve cap member 260 serving to both connect andtighten the unions 230, 240, a technician does not have to operateseparate tightening features such as a pipe tightening collar, or aseparate valve sealing cap in addition to a tightening feature.

Fixed Orifice Plate Orientation

In some embodiments, a display tab 250 can latch onto a size indicationslot 320, such that the display tab 250 prevents any rotational movementof the orifice plate 210. By having the display tab 250 latch onto thesize indication slot 320 on the male union, the display tab 250 can beplaced inside an outermost circumference of the male union (theoutermost circumference can be the circumference of the threaded portionof the male union). A display tab 250 that latches onto the sizeindication slot 320 can position the display tab 250 at a fixedorientation. Sometimes an orifice plate 210 may bend, rotate, tilt, orbend during operation of the orifice wellhead system 100 due to shaking,vibration or other external impacts. Latching the display tab 250 ontothe size indication slot 320 can help affix the orifice plate 210 andreduce displacement of the plate 210. By having a fixed orientation, atechnician can expect the display tab 250 to be visible from a setlocation, such as at a location where a technician stands to operate theorifice wellhead system 100, a pressure sensor, pipe adjustment tools,etc.

In some embodiments, a substantially circular orifice plate 210 can beused. The circular shape of the orifice plate 210 may allow the orificeplate to be encased within the circumference of the valve unions 230,240, valve cap 260, and/or the pipes. Being encased can mean that nopart of planar surface of the orifice plate 215 is exposed outside ofthe flow control valve 120, such that the orifice plate 210 is not bent,twisted, or manipulated by external impact.

In some embodiments, the display tab 250 is connected to the orificeplate 210 on or near the outer circumference of the orifice plate 210,such that no part of the orifice plate 210 extends beyond thecircumference of the male union 230. This configuration can allow thevalve cap member 260 to be placed over the orifice plate 210, tocompletely encase the orifice plate 210.

Sealing

In some embodiments, the valve 120 may be sealed, while minimizing theamount of vacant space between the valve and the valve cap member 260. Amore complete sealing is achieved by minimizing the amount of vacantspace inside the valve cap member 260. Leakage of gas due to poorsealing can compromise the accuracy of the gas flow controldetermination. For a more complete sealing, a mechanical seal such as ano-ring 270 can be used between the orifice plate 210 and the male andthe female unions 230, 240. The o-ring 270 can be made of an elastomerthat can be compressed from its original expanded state. As the spacebetween the male union and the female union 230, 240 is tightened, theo-ring 270 can be compressed to seal off gas passage. The mechanicalseal made of an elastomer, in addition to sealing the space between themale and the female unions 230, 240, can grip the orifice plate 210 inplace and prevent its displacement by exerting a frictional force ontothe place and the union members.

As shown in FIG. 5, the male union member 230 can provide a groove 310for the o-ring, such that the o-ring can be placed in a pre-setlocation. A precise placement of the o-ring 270 can prevent the o-ring270 from being displaced, when the orifice plate 210 is being replaced.The o-ring 270 can remain in the groove 310 and not slide out as thetechnician takes the orifice plate 210 off of the male union 230. Aprecise placement of the o-ring 270 can also help ensure that the o-ringis properly placed to seal off the gas passage, rather than being placedoff-centered or in any other location or orientation that can compromiseits sealing capability.

Retrofitting

As noted above, FIG. 5 illustrates a cut-out view of an embodiment of amale union 320. In this example, the top surface portion 315 of the maleunion includes an orifice plate recess 330 and an o-ring groove 310. Theorifice plate recess 330 can be a recess on the top surface 315 made byforming a perimeter wall 335 to surround the orifice plate 210. Theperimeter wall 335 can be sized to allow an orifice plate 210 to fitwithin an inner circumference of the perimeter wall 335 such that theorifice plate 210 is supported by the orifice plate recess 330 and ano-ring 270 placed in the o-ring groove 310. The perimeter wall 335 canbe sized to allow an orifice plate 210 to be supported by the orificeplate recess 330. The perimeter wall 335 can be sized to allow thecircumference of the female union 240 to fit within an innercircumference of the perimeter wall 335. As shown, the o-ring groove 310can be a cut-out on the top surface portion 315 shaped and sized to fitthe o-ring 270. In some embodiments, as shown in FIGS. 4 and 5, theo-ring groove 310 can be a circular cut-out on the orifice plate recess330.

In some embodiments, an existing flow control valve may be easilyreplaced (retrofitted) with the valve 220 configured for supporting atabbed orifice plate 210 (discussed further below). For example, thevalve 120 in FIG. 1 may include an orifice plate, but there is noexternally visible indication of whether there is an orifice plate inthe valve 120 and, if so, what size the orifice is. Thus, the valve 120may be updated and/or changed without significant reworking of the valve120 or wellhead. For example, a retrofitting process may require onlythat the male union is machined (e.g., to create the size indicationslot 320 for the tabbed orifice plate 210, the orifice place recess 330,and/or the o-ring groove 310) without other adjustments to thepre-existing flow control valve 120 and well head. Accordingly, such aretrofit may be performed without introducing extraneous features, suchas a valve collar or a handle used to tighten the upper pipe 140 and thelower pipe 160, or a valve system having one or more side outlets. Suchextraneous features can also require existing pipes to be replaced inorder to introduce said features.

In some embodiments, multiple orifice plates of different sizes can beused with unions of different threads, with machining of only the maleportion 260. For example, the male union 260 can be machined with agrinding machine, a planer, a lathe, a shaper, etc. to fit orificeplates 210 of different sizes. In some embodiments, the male union 230can be molded and/or manufactured to fit the orifice plates (e.g.,including a size indication slot, an orifice plate recess, and/or ano-ring groove), such that an originally plastic molded male union may beusable with the orifice plates discussed herein. To retrofit an existingvalve, either one of these processes could be used to replace or modifya male union with the size indication slot (and orifice plate recessand/or o-ring groove, depending on the embodiment). Thus, in someembodiments a technician may take out an existing union installed in theflow control valve 120, 220 and adjust, manipulate, or machine only amale union to fit in an orifice plate 210. In other embodiments, thesize indication slot may be part of the female union, such that similaraftermarket and/or manufacturing changes to the female union may be madein order to allow placement of an orifice plate with a display tab asdisclosed herein within a size indication slot of a female union and/orvalve cap member.

As noted above, FIGS. 6A to 6D illustrate example orifice plates havingvarious apertures. Orifice plates 210 having various apertures can beused on the flow control valve 220. A technician can replace an orificeplate 210 currently included in a flow control valve with anotherorifice plate having a different aperture 520. For example, an orificeplate 210A having a smaller aperture 520A in FIG. 6A can be replacedwith an orifice plate 210B having a larger aperture 520B. In someembodiments, orifice plate apertures 520 can have different shapes. Forexample, an orifice plate can have a meshed aperture, a slattedaperture, an aperture having a polygon shape, etc. Orifice sizeindications on the tabs 250 may be in different units (e.g., inches ormillimeter), or may be representative of sizes of the orifices (e.g.,the indications may be whole numbers from 1-6, which indicate orificesizes of 0.75 in, 1.0 in, 1.25 in, 1.5 in, 1.75 in, and 2.0 in,respectively; thus, the technician may more easily determine a relativeorifice size and replace with one that is larger or smaller, as needed,based on these simplified representations of the orifice sizes). Asnoted above, orifice sizes may vary from one implementation to another.Similarly, kits of orifice plates may include varying quantities oforifice plates having varying ranges of orifice sizes. For example, afirst orifice plate kit may include eight orifice plates having orificesizes ranging from 0.4 in to 2.1 in, while a second orifice plate kitmay include four orifice plates having orifice sizes ranging from 1 into 2 in.

What is claimed is:
 1. A flow control valve comprising: a male unioncomprising a male threaded portion and a central aperture configured toallow gas flow within the central aperture, and further comprising a topsurface having a recessed ledge configured to receive an orifice platetherein; a valve cap member comprising a female threaded portionconfigured to receive and threadedly engage with the male threadedportion of the male union; an unthreaded female union having an upperportion sized to fit within an aperture of the valve cap member, thefemale union comprising a central aperture configured to allow gas flowwithin the central aperture; and an orifice plate configured forpositioning between the male union and the valve cap member, such thatthe orifice plate is securedly engaged between the male union and thefemale union when the male union and valve cap member are threadedlyengaged, the orifice plate including a substantially circular platehaving an orifice in a central portion of the substantially circularplate, the orifice plate further including a tab portion extendingsubstantially orthogonal to a plane of the substantially circular plate,the tab portion including a visual indication of a size of the orificein the central portion of the substantially circular plate; wherein themale threaded portion includes a size indication slot extending acrossall of threads of the male threaded portion along less than twentypercent of an outer circumference of the male union, the size indicationslot sized to allow at least a portion of the tab portion of the orificeplate to be enclosed between threads of the female threaded portion andthe size indication slot of the male threaded portion.
 2. The flowcontrol valve of claim 1, wherein the orifice plate is securedly engagedbetween the male union and the female union.
 3. The flow control valveof claim 1, wherein the flow control valve further comprises a sealingmeans for sealing a space between the male union and the valve capmember.
 4. The flow control valve of claim 1, wherein the flow controlvalve further comprises a sealing means for sealing a space between themale union and the female union.
 5. The flow control valve of claim 4,wherein the sealing means is an o-ring.
 6. The flow control valve ofclaim 1, wherein the recessed ledge further comprises an o-ring groovecontaining an o-ring, the o-ring groove being shaped and sized to fitthe o-ring.
 7. The flow control valve of claim 1, further comprising asecond orifice plate having a different size orifice than the orificeplate, the second orifice plate configured to replace the orifice platewithin said recessed ledge.
 8. The flow control valve of claim 1,wherein the tab portion of the orifice plate has a width of betweenabout 0.3 and 1.5 inches.
 9. The flow control valve of claim 1, whereinthe orifice plate has an orifice diameter of between about 0.3 and 3.0inches.
 10. The flow control valve of claim 9, wherein the orifice platehas an orifice diameter of between about 0.4 and 2.1 inches.
 11. Theflow control valve of claim 1, wherein the unthreaded female unioncomprises a lower portion sized to be received within the recessed ledgeof the male union.
 12. A retrofit kit for a flow control valve in awellhead system, the retrofit kit comprising at least each of thebelow-listed components packaged together for delivery to a user forretrofitting a flow control valve: a plurality of interchangeableorifice plates each including a substantially circular plate having anorifice in a central portion of the substantially circular plate; and atab portion extending substantially orthogonal to a plane of thesubstantially circular plate, the tab portion including a visualindication of a size of the orifice in the central portion of thecircular plate, wherein at least two of the interchangeable orificeplates have orifices of different sizes; and, a male union comprising amale threaded portion, a top surface, and a central aperture configuredto allow gas flow within the central aperture, the top surface of themail union having a recessed ledge configured to receive theinterchangeable orifice plates therein, the male union furthercomprising a size indication slot extending across all threads of themale threaded portion along less than twenty percent of an outercircumference of the male union, the size indication slot sizedconfigured to allow at least a portion of the tab portion of the orificeplate to be enclosed between threads of a female threaded portion andthe size indication slot of the male threaded portion; wherein the maleunion is configured to replace a widely used male union of existinglandfill flow control valves.
 13. The retrofit kit of claim 12, whereinthe tab portion of the orifice plates has a width of about 0.5 inches.14. The retrofit kit of claim 12, wherein the retrofit kit furthercomprises a sealing means for sealing a space between the male union andthe interchangeable orifice plates.
 15. The retrofit kit of claim 14,wherein the sealing means is an o-ring.
 16. The retrofit kit of claim15, wherein the top surface of the male union is shaped and sized to fitthe o-ring.